Fig. 6. Mos does not facilitate MPF activation in the second meiosis. Oocytes were stimulated by progesterone. At 50% GVBD, the oocytes that did not undergo GVBD were transferred in cycloheximide, and left in this medium for all the experiment. In these conditions, oocytes that underwent GVBD were arrested in interphase 1 hour later. They were then injected with GST-cyclin B1 alone (B1), or both GST-cyclin B1 and MBP-Mos (B1+Mos). Groups of three oocytes were collected at the indicated times and submitted to a GST pull-down assay, followed by a histone H1 kinase assay. The whole final reaction mixture was resolved by SDS-PAGE, and phosphorylated histone H1 was revealed by autoradiography. As a control, the equivalent of one immature oocyte (stage VI) and one mature oocyte (control M) are shown. Lanes 3-8, GST-cyclin B1 at 100 µg/ml was injected per oocyte; lanes 9-14, GST-cyclin B1 at 50 µg/ml was injected per oocyte; lanes 6-8 and 12-14, MBP-Mos at 20 µg/ml was injected per oocyte.